Surface acoustic wave devices (SAW devices) utilizing surface acoustic waves that concentrate their energy only at the surfaces of crystalline substrates involve propagation velocities slower than electromagnetic waves by about 10−5, and the devices can be downsized. Accordingly, they are recently applied to filters, oscillators, delay elements, and the like in broad fields including TVs, VTRs, and communications equipment. Among them, the surface acoustic wave devices are widely used for video frequency filters, etc., typically applied to TVs and VTRs.
A surface acoustic wave device for video consists of a surface acoustic wave element with metal electrodes formed on a piezoelectric substrate to excite surface acoustic waves and a plastic package with a lead frame to realize miniaturization, light weight, and work rationalization. The plastic package is made of a plastic casing base and a plastic cap. The plastic casing base is integrally formed with the lead frame that is inserted into the casing and has a die pad part on which the surface acoustic wave element is mounted and bonding pad parts. The die pad part is positioned within the casing of the plastic base and to which the surface acoustic wave element is bonded with an adhesive. The surface acoustic wave element is electrically connected to the bonding pad parts with wire bonding. In a last assembling process, the plastic cap is fixed to the plastic casing base with an adhesive, to close the inside of the casing.
However, the surface acoustic wave device employing the conventional plastic package has a below-mentioned problem. Namely, the conventional plastic package employs thermosetting epoxy resin to meet a SAW filter packaging quality. Generally, a material color of the epoxy resin is mainly black. Accordingly, when the plastic cap and plastic casing base are assembled into the plastic package, they have the same color tone to hardly identify the front and back faces of the surface acoustic wave device. Conventionally, the plastic cap and plastic casing base are provided with slightly different plan shapes to distinguish them from each other, or they are distinguished from each other according to a manufacturer name, production number, etc., printed thereon. They, however, are insufficient as clarification standards and involve a risk of misjudging the front and back faces.
In particular, when the plastic package is inserted into a printed board and the like, it is necessary to identify the front and back faces of the plastic package by directly looking at the same from a top-face direction. Namely, the front and back faces are judged from a side view of the plastic package. Accordingly, the clarification standards such as the slight difference between the front and back shapes and the printing are useless, and inserting direction errors frequently occur.